The invention relates to video processing in general. More particularly, the invention relates to a method and apparatus for transcoding Digital Video (DV) signals to Motion Picture Experts Group (MPEG) signals for storage on a Digital Versatile Disc (DVD).
Digital video is becoming increasingly popular because of its capability of delivering high picture quality. One problem with digital video, however, is the amount of digital data which is necessary to represent an image with high levels of detail. This in turn creates problems with storing the digital data, and transporting the digital data between individual devices (e.g., from one computer to another over a network). Consequently, various compression technologies have been developed to reduce the amount of digital data necessary to represent analog video signals, while still maintaining the high levels of quality associated with digital video. One such compression technology was introduced by Sony Corporation titled xe2x80x9cSpecifications of Consumer-use Digital VCRs using 6.3 mm magnetic tape,xe2x80x9d December 1994, HD Digital VCR conference (xe2x80x9cDV standardxe2x80x9d).
While the DV standard helps reduce the amount of digital data necessary to represent a video signal, a recent technology has emerged which permits larger amounts of digital data to be stored on an optical disc having the size of a conventional Compact Disc (CD). This new technology is referred to as Digital Versatile Disc (DVD), and provides the capability of storing up to 4.7 Gigabytes of data per disc. This represents a significant increase over previous storage techniques. DVD thus offers a desirable medium for storing digital video in general, and DV encoded signals in particular.
A problem occurs, however, while attempting to store DV encoded video signals to DVD media. DVD is only capable of storing digital video signals compressed according to a particular compression standard such as the International Standards Organization/international ElectroTechnical Committee (ISO/IEC) Motion Picture Expert Group Two (MPEG-2) 13818-2, titled xe2x80x9cInformation technologyxe2x80x94Generic coding of moving pictures and associated audio information: Video,xe2x80x9d 1994. Consequently, the DV encoded signal must first be decoded using a DV decoder, and then re-encoded using an MPEG encoder, prior to being stored on DVD media. The process of re-encoding a video signal is often referred to as xe2x80x9ctranscoding.xe2x80x9d
Conventional DV to MPEG transcoding techniques are unsatisfactory for a number of reasons. First, conventional transcoders require that the DV encoded signal be decoded to the spatial domain (e.g., a set of 8xc3x978 pixel or xe2x80x9cPELxe2x80x9d values from a video frame) represented by some arbitrary intermediary format such as xe2x80x9cRGBxe2x80x9d. RGB is a color model in which colors are specified as intensities (between 0.0 and 1.0, if floating point representation is used, or between 00 and 0xFF for 8-bit integer hex representation) of the three CRT monitor primary colors: red, green, and blue. The pixel values are then re-encoded in accordance with the MPEG standard. The need to reduce the DV encoded signal to the spatial domain, however, is time consuming and expensive in terms of processing cycles. This prevents DV encoded signals from being recorded to DVD in real-time or near real-time. Further, it increases the overall cost of the transcoder, since large amounts of memory are necessary to buffer the DV encoded signals while the transcoding process is being performed.
In view of the foregoing, it can be appreciated that a substantial need exists for a new video transcoder which solves the above-discussed problems.
One embodiment of the invention comprises a method and apparatus for transcoding a digital video signal. A first set of bits encoded in a first encoding format are received. The first set of bits are decoded to discrete cosine transform (DCT) coefficients. The DCT coefficients are transformed into an intermediate exchange format. The transformed DCT coefficients are encoded using a second encoding format.